Catheters are slender tubes widely employed in the medical field for insertion into body passages, vessels or cavities. They are employed for passing fluids, draining fluids, making examinations, etc.
It is generally desirable that catheters be radiopaque because it is often necessary to determine the precise location of a catheter within its host by X-ray examination. In addition, it would be advantageous if catheters were optically transparent so that the flow of fluids therethrough could be observed.
There has been extensive research over a long period to improve the properties of catheters, including the properties of X-ray opacity and optical transparency. This research is documented, for example, in the patent literature.
U.S. Pat. No. 2,212,334 issued to Wallerich in 1940 describes early attempts to produce an optically transparent catheter having some radiopaque properties. In this patent, Wallerich describes the extrusion of a plastic cellulose material through a tubular molding die coupled with forcible injection of small quantities of X-ray opaque material at uniform brief intervals to vary the X-ray opacity of the extruded catheter at regular intervals.
U.S. Pat. No. 2,857,915 issued to Sheridan describes efforts to produce catheters which were normally transparent to visible light but having an integral continuous opaque stripe running along the length of the catheter. The polymers suggested by Sheridan included nylon, polyester, polyethylene, and vinyl.
The art of adding a radiopaque stripe to a catheter was further refined as described in U.S. Pat. Nos. 4,027,659 and 4,105,732 issued to Slingluff. Slingluff added a highly conductive material, as well as a radiopaque material, to the stripe running along the length of the catheter. Thus, the stripe could be employed for observing the catheter's location with x-rays and for electrically grounding the catheter to allow discharge of any electrostatic charges built up during use of the catheter.
In U.S. Pat. No. 3,605,750, issued to Sheridan et al., catheters having radiopaque distal end portions are described. These are made X-ray opaque by fusing a plastic annulus containing X-ray opaque pigment onto a preformed catheter tube.
U.S. Pat. No. 3,529,633 issued to Vaillancourt describes the many prior efforts to provide a catheter which was optically transparent and yet had radiopaque properties. In this patent, Vaillancourt suggests that catheters be formed from fluorinated polymers, such as polytetrafluoroethylene, having an adequate quantity of precipitated barium sulfate to provide X-ray opacity with a minor portion of the catheter or "window" remaining clear and transparent.
Greyson, in U.S. Pat. No. 3,608,555, suggests incorporating an X-ray opaque substance having an index of refraction close to that of the polymer to provide radiopacity with sufficient optical permeability to permit viewing of fluids within the catheter. Greyson also suggests that crystallization should be minimized for crystalline-forming polymers, such as perfluorocarbon resins.
In U.S. Pat. No. 3,618,614, Flynn suggests multiwall surgical tubing having an inner relatively thick transparent tube encased in a relatively thin, visually transparent, outer shell containing a radiopaque material. Thus, X-rays pass through the lateral edges of the composite tube through a relatively long path at the side edges of the tubing while the central portion remains substantially transparent.
Flynn suggests the addition of certain radiopaque plasticizers to vinyl resins employed in the formation of medical-surgical tubing in U.S. Pat. No. 3,645,955. These plasticizers include halogenated benzoates, such as alkyl 2,5-diiodobenzoates, alkyl or alkoxyalkyl 2,3,4,6-tetraiodobenzoates, or mixtures thereof.
In U.S. Pat. No. 3,336,918, Jeckel describes the use of polyurethane coatings containing radiopaque metal powders such as tin, lead and bismuth, for use in catheters. It had previously been found that the addition of such radiopaque metals accelerated the urethane reaction limiting the pot-life thereof. The specific invention described by Jeckel in this patent is the use of small amounts of diglycolic acid to control or halt the catalytic action of the heavy metal powder on the urethane reaction thereby lengthening the pot-life.
In U.S. Pat. Nos. 3,749,134 and 3,901,829, Slingluff describes yet further attempts to produce catheters which are optically transparent and radiopaque. In these patents, Slingluff suggests blending a small amount of a diol of tetrabromophthalic anhydride and a plasticizer with the thermoplastic resin employed in forming the catheter. The diol is distributed throughout the entire wall of the tubing rendering it radiopaque or, alternately, the diol can be limited to certain areas or zones or added in any desired pattern. The use of such diols and plasticizers is suggested with a wide variety of thermoplastic resins, such as polyethylene, vinyl polymers, nylon, flexible polyurethane, etc.
Goossens et al. suggest that optically clear radiopaque catheters can be formed from certain terpolymers in U.S. Pat. No. 4,182,787. These are terpolymers of polycarbonatepolydiorganosiloxane having carbonate, halocarbonate and polydiorganosiloxane constituents.
U.S. Pat. No. 4,282,876 issued to Flynn describes still . another polymer composition intended to produce a combination of optical clarity with radiopacity for catheters. The polymers described are polyurethane resins, alone, or combined with vinyl resins, and having alkyl or alkoxyalkyl 2,5-diiodobenzoates, 2,3,4,6-tetraiodobenzoates or mixtures thereof added to provide radiopacity.
Generally, the suggestions described above have involved combining a structural resin for the catheter with a second component, intended to affect the X-ray opacity, in a physical blend. Unfortunately, it has been discovered that such physical blends suffer from certain drawbacks. For example, the material blended in to add radiopacity often can be leached from the material. In extreme cases, the material can be leached from the catheter and absorbed systemically by the host.
In certain instances, as exemplified by the use of added barium sulfate, the incorporation of the added material has resulted in the creation of physical non-uniformities in the polymer blend causing the walls of the catheter to be abrasive. As a result, insertion and removal forces are increased which, in some cases, may result in patient discomfort.
The Goossens et al. patent referred to above, while not suggesting a mixture but instead suggesting a polymer having the properties of radiopacity and optical transparency, suffers from still other drawbacks. For example, it has been found that the Goossens et al. polymer exhibits stiffness which is not dissipated when a catheter made from this material is inserted into the blood vessel of a host.